Device for avoiding whiplash injuries

ABSTRACT

A device for counteracting whiplash injury to a person sitting in a seat ( 1 ) which can occur due to a rapid change in velocity, such as a collision, primarily from the rear, or similar. The device is characterized by containing means of allowing controlled displacement of the entire seat ( 1 ) against the direction of travel during rapid change of velocity, that the seat ( 1 ) is provided with control devices which are arranged to give the seat and its occupant an essentially simultaneous and essentially linear movement against the direction of movement and/or an essentially arcuate movement, and that the seat ( 1 ) is arranged to stay in a rear position after the change of velocity.

TECHNICAL AREA

This invention refers to a device and a method for counteracting injuryto a person sitting in a seat in vehicle, primarily a so called whiplashinjury, which can occur due to a rapid change in velocity, such as acollision, primarily from the rear, or similar.

BACKGROUND OF THE INVENTION

A whiplash injury is a soft tissue injury which can occur on account ofviolent acceleration and/or deceleration applied to the cervical spine.The classic case where these kinds of neck injuries occur is whensitting in a car which is subjected to a rear-end impact, but can alsooccur in other activities than car driving, such as in participating incertain sports.

According to the Folksam insurance company, 16,000 claims are sent tothe insurance companies every year because o rear-end impacts in Swedenalone. Of these cases, 1,500-2,000 sustain permanent injury and 100-200have to be given a disability pension. Whiplash injury is the mostcommon type or injury resulting in compensation from the insurancecompanies. When head restraints, popularly termed head rests, becamestandard in cars, there were considerable hopes that whiplash injurieswould disappear. The disappointing result was that the risk of permanentinjury only fell by less than 20%, which shows that the problem largelyremains.

Several researchers agree that the following factors and situations areof decisive importance for the question of whether a collision willcause whiplash injury or not.

The distance between the head and the head restraint, and the verticallocation of the head restraint.

The magnitude of the collision, the crash pulse.

The stiffness of the car. A stiff car gives greater acceleration, andthus higher forces.

The angle of the backrest.

The muscular strength of the individual, in combination with the lengthof the cervical spine.

If the person is prepared, and tensions his neck muscles back againstthe head restraint before the collision, the risk of whiplash injury isminimal.

Small children who travel in rearwards-facing child seats are subjectedto the same or greater forces in a front-end crash than adults who aresubjected to a rear-end collision. Despite this, children seldom sufferfrom neck injury in a front-end collision. Children very seldom sustainwhiplash injuries.

Women are subjected to about a 50% greater risk than men of sufferingwhiplash injury in a rear-end collision. Statistics from the same typeof car (Folksam).

It has been found that the injury frequency is lower in older cars,where the seat backrest collapses in a rear-end collision, compared withnewer cars with stronger seats (VTI).

People in the back seat are only subject to half the risk of sustainingneck injuries compared with people in the front seat. This is despitethe fact that head restraints are frequently not provided for the rearseats. (Folksam).

“Bouncy” seats entail a greater risk of whiplash injury (ChalmersUniversity of Technology).

About 25% of all whiplash injuries occur in front-end collisions(Folksam).

Passengers in a 4-door Volvo 240 have a 20% higher incidence of whiplashinjury compared to passengers in a car which is identical, except that.it only has 2 doors. The only difference is that on the 2-door car, theB pillars are located 270 mm further back, compared with the 4-doormodel. This affects the position of the upper seat belt anchorage(Folksam).

The last five points indicate that the risk of sustaining a whiplashinjury are greatest when the head is thrown forwards as far as it willgo (hyperflexion), which occurs after about 400 ms. Regardless of whenthe injury occurs, the risk is considerably reduced if the accelerationof the seat is minimized.

In recent years, research in this area has been intensified, which hasled to new theories and experience related to the cause of whiplashinjury. Several theories and initiatives have been found to be incorrectand have therefore now been rejected. This means now that there are oldtechnical solutions which do not solve the problem.

Since the person sits completely still at the start of the crashsequence, the solution should be based on a system or device whichreduces the acceleration to less than 4 g, since it has been found thatwhiplash injury is avoided at accelerations below 4 g. This has beendemonstrated in experiments on volunteers (please refer to “Comparisonof head-neck kinematics during rear-end impact between standard HybridIII RID neck, volunteers and pmtos”) By allowing the entire seat to movebackwards on a sledge-like element in the car during the instant ofcollision, the acceleration can be reduced to less than 4 g. Throughlower acceleration, lower forces are experienced, which leads to astrongly reduced risk of injury.

In crash tests performed by the VOLVO Car Corporation (VOLVO TechnologyReport on. 2, 1996), acceleration and velocity values in a typicalrear-end collision were found to have the values shown in diagrams 1 and2.

FIGS. 3-8 show the crash sequence in the first 400 milliseconds, whereFIG. 3 shows the crash sequence at time 0 milliseconds (ms), where theperson is in the initial position and is thus not affected by anyacceleration due to collision etc. FIG. 4 shows the crash sequence at atime of 50 ms, when the acceleration has reached its peak after only 10ms. The speed of the car increases more or less linearly and has reachedits top speed after about 50 ms on account of the collision. The bodyinitially moves straight backwards without any mutual displacement ofmembers. At 50 ms, the person's neck muscles begin to tense in a reflexaction to counteract the rearwards movement of the person's head. Thisis regarded as being a decisive factor when the sequence is studied. Allstudies involving acceleration greater than 5 g have been a cone ondummies, cadavers etc. FIG. 5 shows the crash sequence at a time ofabout 100 ms, when the relative movement begins. The shoulders stop andthe head and lower body continue to move backwards. This has been provenby researchers at the Chalmers University of Technology and others. Theyfound that this is because the backrest is stiffer at the top, due tothe cross beam in the backrest frame which unites the right and leftsides of the backrest. At the same time, the mass of the body is greaterin the pelvic area than in the shoulder area. There are theories thatwhiplash injury is caused by this effect, due to the rapid increase inpressure in the cervical spinal canal, which occurs when the head movesbackwards and the volume of the cervical spinal canal decreases in avery short space of time due to the extension. This leads to an increasein pressure in the cervical spinal canal which can cause bleeding in theblood vessels around the spinal canal (myelorrhagia). Experiments havebeen performed on pigs at Chalmers University of Technology, in whichthe increase in pressure in the cervical spinal canal due to forcedrapid extension was measured. Another probable source of injury would bethe damage caused by the shear stress in the neck, which occurs when thehead wants to move back relative to the shoulders. This effect issimilar to a pack of cards lying on a table when you move the upper partof the pack sideways. The cards illustrate the disks in the cervicalspine. Between 100-200 ms, the neck muscles have reached their maximumforce in trying to stop the rearwards movement of the head. This muscleforce represents a bending moment equivalent to a force of up to 300 Nat eye height. FIG. 6 shows the crash sequence at 200 ms when the headhas moved back as far as it goes, relative to the backrest and headrestraint. The neck muscles are still at maximum tension. The backrestand head restraint are bent back to a maximum, and like a big spring,they will soon throw the head and torso forwards with great force. FIG.7 shows the crash sequence at 300 ms, when the head has about twice thespeed of the car and seat. The neck muscles are still at maximumtension, which means that the acceleration of the head continues. It isprobable that the head reaches nearly three times the speed of the carand seat when the backrest is “bouncy”. This is because the backrest andneck muscles interact in an unfortunate manner. FIG. 8 shows the crashsequence at about 400 ms, when the head reaches its normal stoppingpoint. The torso suddenly stops when it meets the stiff seat belt. Atthis time, the head continues forwards, with considerableover-extension. Several facts indicate that it is here that the whiplashinjury occurs. This would explain the whiplash injuries which occur infront-end collisions and would also explain why the incidence ofwhiplash injury in a 4-door Volvo 240 is higher than in a 2-door, duringa rear-end impact.

From this reasoning follows the thesis that it is very important toreduce the acceleration and thus to reduce the forces in a rear-end carcollision. One way to do this is to allow the entire seat to movebackwards in the car, in a controlled and damped movement, where theseat remains in a rearward position.

One solution is demonstrated in WO 96/16834, which is mainly based onbackrest movement. The solution lacks a trigger mechanism, whose purposeis to release the rearward movement. This gives the seat a purely linearmovement, which would appear to be parallel with the floor of the car,and is only intended to delay the time until the occupant's headcontacts the head restraint. It can primarily be described as a springwhich gives a forward and rearward movement. Dampers and plasticizingsolutions are described, however. No linear-arctuate movement ortrajectory are described. The entire solution in WO 96/16834 is based onthe assumption that the occupant's back, neck and head are not supportedand will be subjected to a considerable impact with a certain delay,because of the force against the backrest, which could cause a whiplashinjury. The occupant and the seat are initially at rest, with no otherforces acting upon them than gravity. When the floor of the car suddenlybegins to accelerate, the back and backrest are carried along as well.The present invention and the invention described in WO 96/16834 do nothave the same assumption about the fundamental reasons for why whiplashinjury occurs. This means that the solution presented in WO 96/16834 isintended to solve a problem which is not foreseen in this invention.

The invention in U.S. Pat. No. 3,992,0.46 is intended to reduce injuryin a rear-end collision. This invention is also largely based on linearmovement in parallel with the floor of the car. The invention in U.S.Pat. No. 3,992,046 and the present invention do not solve the sameproblem, since one refers to front-end collisions and the other refersto rear-end collisions.

The invention in WO 93/01950 is also only intended to reduce injury infront-end collisions. The invention lacks a trigger mechanism and isbased on a seat track which differs from the present invention. Inaddition, the invention in WO 93/01950 does not remain in its triggeredposition after it has been triggered.

The invention in U.S. Pat. No. 3,802,737 is a totally differenttechnical solution. In that solution, the head restraint has a higheracceleration than the floor. The present invention is based on theopposite principle, i.e. it reduces the acceleration of the headrestraint. The solution in U.S. Pat. No. 3,802,737 is mainly based ondeformable sections in the backrest. In that solution, the headrestraint is moved backwards and upwards in the car. In the presentsolution, the movement is backwards and downwards, or movement backwardsat the same time as the front of the seat moves upwards.

The above description of previously-known technology gives a collectionof inventions which all refer to some extent to injuries sustained incollisions. Another major and important difference consists of theproblems which these inventions are intended to solve. In thisconnection, it is important to point out that one consequence ofintensified research in this field is increased knowledge about whiplashinjuries and their origins, which has led to and constantly leads to newproblem formulations and deeper nuances of old problem formulations.This means that there are considerable differences between currentproblem formulations and old ones.

THE PURPOSE AND MOST IMPORTANT CHARACTERISTICS OF THE INVENTION

The fact that the mechanisms of the car, the seat and the head restraintall interact with the neck muscles is a phenomenon which has notpreviously been studied in depth. Almost all studies involvingacceleration greater than 5 g have been done on dummies or cadavers,which is obviously a limitation in this area. New results indicate, asnoted above, that: it is the interaction between the occupant and theseat which cause whiplash injuries. The main purpose of the invention isto reduce the acceleration to which the body is subjected after theincidence of the collision to less than 4 g, since it has been foundthat whiplash injuries occur in collisions exceeding 5 g.

These new findings, combined with this invention, will lead to fewerinjuries. The purpose of this invention is achieved through a device anda method intended to counteract the occurrence of whiplash injury to aperson sitting in a seat, which could occur through a rapid change invelocity, such as in a collision essentially from the rear or similar.The characteristics of this invention are that the arrangement containsa means whereby the seat will move in a controlled manner against thedirection of movement during a change in velocity, and that the seat isprovided with guidance devices which are intended to give the seat andthe person sitting in it an essentially simultaneous and essentiallylinear movement against the direction of movement and/or an essentiallyarcuate movement, and that the seat is arranged so that it will remainin its rearward position after the change in velocity.

When the seat moves backward, there is a risk that it will collide witha knee belonging to a rear-seat passenger. This can be reduced if theseat is given extra inclination when the device is triggered, whichleads to a reduction in injury of the rear-seat passengers.

These purposes have been solved in this invention, by means of thecharacteristics described in the patent claims.

DESCRIPTION OF THE DRAWINGS

The invention will be described below with reference to the preferredembodiments shown in the attached drawings.

FIGS. 1 and 2 show the values of acceleration and velocity during atypical rear-impact collision.

FIGS. 3-8 show the crash sequence during the first 400 milliseconds.

FIG. 9 shows a preferred embodiment of a device, in untriggeredposition, intended to reduce injury, mainly the so called whiplashinjuries referred to in the description of the invention.

FIG. 10 shows a preferred embodiment of the same device as in FIG. 1,but in the triggered position.

FIG. 11 shows an alternative preferred embodiment, in untriggeredposition, intended to reduce injury, mainly the so called whiplashinjuries referred to in the description of the invention.

FIG. 12 shows a preferred embodiment of the same device as in FIG. 11,but in the triggered position.

FIG. 13 shows how a shock absorber with adjustable damping effect can beconstructed by means of two disks provided with holes.

FIG. 14 shows a preferred embodiment of how a shock absorber withadjustable damping can be constructed by means of a tapering space forthe damping piston.

FIGS. 15-19 show preferred embodiments of different variants of the wayin which the tracks can be designed to give the seat a rearwardinclination.

DESCRIPTION OF PREFERRED EMBODIMENTS

The preferred embodiment in FIGS. 9-12 illustrate implementations in themotor vehicle field, more specifically in a passenger car. It should benoted that the invention is also intended for use in buses etc. althoughthe description primarily refers to the use of the invention inpassenger cars. The concept of “against the direction of travel” refersto the direction in which the car normally moves when it reverses. Thefirst preferred embodiment in FIG. 9 shows a device intended to reduceinjury, mainly the so-called whiplash injuries referred to in thedescription of the invention, sustained by a person sitting in seat 1,which could be caused by a sudden change in velocity, such as in acollision essentially from the rear or similar. Its technicalcomposition contains a means which permit controlled movement of theentire seat 1 or sections thereof, during a change in velocity, againstthe direction of travel and upwards or downwards. Seat 1 is providedwith a guidance element, which is arranged to give the seat and itsoccupant an essentially simultaneous and essentially linear movementagainst the direction of travel and/or an essentially arcuate movement.

The purpose of the arcuate movement is to arrange the seat in a positionwhich is associated with a lower risk of sustaining whiplash injury. Thecharacteristic of this position is that the seat takes up an inclinedposition such that the rearward inclination of seat 1 is greater thanthe inclination of the seat in the normal case. The arcuate movementwhich results from the leaning position can be achieved by a number ofdifferent means.

In general, at the end of the movement, the rear of the seat is closerto the floor of the car in relation to the front of the car. It is therelative movement in height between the front section and the rearsection of the seat which provides this effect. The movement can beimplemented in a number of different ways:

The front section of the seat moves upward at the same time as theentire seat moves backward in the horizontal direction.

The rear section of the seat moves downward at the same time as theentire seat moves backward in the horizontal direction.

Both the front section and the rear section of the seat move downward,but the rear section moves down more than the front section, at the sametime as the entire seat moves backward in the horizontal direction.

Both the front section and the rear section of the seat move upward, butthe front section moves up more than the front section, at the same timeas the entire seat moves backward in the horizontal direction.

The front section of the seat moves upward at the same time as the rearsection of the seat moves downward, at the same time as the entire seatmoves backward in the horizontal direction.

(Downward refers to a direction aligned essentially at right anglestowards the floor of the vehicle) Upward refers to the oppositedirection.

The desired inclination of the seat can be achieved by a number ofsolutions. One way is to design a arctuate section, such as part of anarc of constant or varying radius. This section can be connected to anessentially straight segment. The preferred embodiment has beenimplemented as an intermediate section 2 (also called centre section),fixed between the ordinary attachments 3 of the seat 1 on the floor ofthe car. The seat 1 can not move backwards and upwards/downwards untilthe trigger mechanism 4 has tripped. The backwards movement isfacilitated by fixing a rolling device 5, such as wheels, to seat 1 andallowing these to roll along one or several tracks 6 in the preferredembodiment. It should be noted that neither intermediate section 2 nortracks 6 necessarily have to be made in one piece, they could very wellconsist of four sections, for example, each containing one rollingdevice, whose extent and size are such that each rolling device can movein such a way that the purpose of the invention is achieved.

Since the rearward inclination of the seat after the device hastriggered is of central importance to the invention, a description ofhow this can be technically achieved is attached. FIGS. 15-19 containschematic diagrams illustrating critical sections of rolling device 5and the design of track 6. The front section of the seat is on the leftof the figures. The device is shown in the figures in the untriggeredposition. It should be noted that all figures show a horizontalorientation of track 6, seen from the movement of rolling device 5. Itis not necessary for the track to consist of single elements, it canconsist of two or more track elements whose purpose is to supportrolling device 5 when it moves, as shown in the figure. FIG. 15illustrates how the front section of the track shows an essentiallyhorizontal segment 20, attached to a segment 21 which is bent upwardsand a rear track section with an essentially horizontal segment 22.

FIG. 16 illustrates how the front section of the track shows anessentially horizontal segment 23 and a rear track section with anessentially horizontal segment 24, attached to a segment 25 which isbent obliquely downward.

FIG. 17 illustrates how the front section of the track shows anessentially horizontal segment 26 attached to a segment 27 which is bentobliquely downward and a rear track section with an essentiallyhorizontal segment 28, attached to a segment 29 which is bent obliquelydownward. The difference between segments 27, 29 which are bentdownward, is that the rear one 29 is bent downward more than the frontone 27.

FIG. 18 illustrates how the front section of the track shows anessentially horizontal segment 30 attached to a segment 31 which is bentobliquely upward and a rear track section with an essentially horizontalsegment 32, attached to a segment 33 which is bent obliquely upward. Thedifference between segments 31, 33 which are bent upward, is that thefront one 31 is bent upward more than the rear one 33.

FIG. 19 illustrates how the front section of the track shows anessentially horizontal segment 34, attached to a segment 35 which isbent obliquely upward, and a rear track section with an essentiallyhorizontal segment 36, attached to a segment 37 which is bent obliquelydownward.

The use of these track configurations will lead to seat 1 taking up amore rearward position after the device has triggered than before it hastriggered. It should be noted that the essentially horizontal segment inFIGS. 15-19 can be omitted to allow seat 1 to begin to moveupward/downward at once when the device has triggered, which also leadsto rearward movement. In addition, it is possible to give theessentially horizontal segment a certain inclination. One purpose of theessentially horizontal segments is to brake the seat during the timethat seat 1 is moved. Braking will cause the head of the occupant tocome into contact with the head restraint, which will catch up the headand give it support during continued movement of seat 1 upward ordownward, depending on the track configuration chosen as above.

The trigger mechanism 4 can be of a previously known type. It can betriggered by force, acceleration etc. During movement of seat 1 backwardand upward/downward, the movement is damped so that the occupant of seat1 is not subjected to the same change of velocity to which the car orbus is otherwise subjected. At the end of the rearward movement, theseat thus takes up a position which is more rearwardly inclined than wasthe case before the seat 1 was triggered.

Seat 1 is designed to remain in the rearward position after the changeof velocity. However, slight forward motion due to the seat backrestspringing back from a state of elastic deformation is not prevented.

Damping of the movement is achieved by means of one or several dampingdevices, such as one or several traditional shock absorbers 8 or one orseveral dampers whose damping effect is a function of acceleration ormovement. An alternative way of implementing a damping device could beto use assemblies containing plasticizing elements, which plasticize ontriggering. FIG. 4 shows seat 1 after the triggering device 4 hastriggered and the seat 1 has been moved rearward.

An analysis of the design of this seat is given by reference to the twoexamples given below, please refer to FIGS. 1 and 2, where a, v, t, Fand m s correspond to units of acceleration, velocity, time, force,mass, and distance respectively.

A first example demonstrating the capacity of the present invention toreduce the acceleration of a seat contained within a vehicle acted uponby an external force is as follows. Where a=Δv/Δt, Δv=11 km/h=3.06 m/s,and Δt=0.05 s, a=(3.06 m/s)/(0.05 s)=61 m/s². Hence, a body which isaccelerated from rest to a velocity of 11 km/h in 0.05 seconds isexposed to an acceleration of 61 m/s². Assuming constant accelerationwhere v_(avg)=(v_(initial)+v_(final))/2, the distance the body travelsduring this time is given by the relationship s=v_(avg)*t=[(3.06m/s)/2]*0.05 s=0.0765 m. Hence, a body which is accelerated from rest at61 m/s² to a velocity of 11 km/h travels a distance of 0.0765 m in 0.05seconds. If the present invention moves the seat backward 90 mm (0.09 m)during the rear-end impact the acceleration will occur over a totaldistance equivalent to 0.0765 m+0.09 m=0.1665 m. Similarly, the timeover which the acceleration will occur is extended as determined byt=s/v_(avg)=0.1665 m/[(3.06 m/s)/2]=0.1085 seconds. The extendeddistance and time over which acceleration occurs corresponds to anacceleration calculated as a=Δv/Δt=(3.06 m/s)/0.1085 s=28 m/s². Hence,the present invention reduces acceleration from 61 m/s² to 28 m/s², i.e.by 54%. At a result, a person sitting in the seat is subjected to 54%less force during the rear-end impact.

A second example demonstrating the capacity of the present invention toreduce the acceleration of a seat contained within a vehicle acted uponby an external force from 10 g to 4 g is as follows. In a relativelyheavy collision, velocity increases from 0 km/h to 18 km/h in 50 ms.Where a=Δv/Δt, Δv=18 km/h=5 m/s, and Δt=0.05 s, a=(5 m/s)/(0.05 s)=100m/s². Hence, a body which is accelerated from rest to a velocity of 18km/h in 0.05 seconds is exposed to an acceleration of 100 m/s² orapproximately 10 g's. Assuming constant acceleration wherev_(avg)=(v_(initial)+v_(final))/², the distance the body travels duringthis time is given by the relationship s=v_(avg)*t=[(5 m/s)/2]*0.05s=0.125 m. Hence, a body which is accelerated from rest at 100 m/s² to avelocity of 18 km/h travels a distance of 0.125 m in 0.05 seconds. Ifacceleration is limited to 4 g's=39.2 m/s², the time to reach a velocityof 5 m/s is given by Δt=Δv/a=(5 m/s)/(39.2 m/s²)=0.127 seconds.Similarly, the distance traveled to reach a velocity of 5 m/s at anacceleration of 39.2 m/s² is given by s=v_(avg)*t=[(5 m/s)/2]*0.127s=0.32 m. The seat movement required to reduce acceleration of the seatfrom 10 g's to 4 g's is equal to the difference between the 4 g and 10 gdeceleration distances, or 0.32 m−0.125 m=0.195 m.

If the seat moves back 195 mm, the acceleration is reduced from 10 g to4 g. If the seat moves a shorter distance in an initially linearmovement which is then transformed into a circular movement, this meansthat the head restraint moves 195 mm, the same effect is obtained at thesame time as the risk of hitting one of the rear seat passengers isreduced. The controlled change of position of the entire seal 1 during achange of velocity is arranged to be limited to 20-400 mm, i.e. theleast change of movement in one application can be 20 mm and thegreatest change in another implementation can be 400 mm.

A sensor 9 is arranged to detect the position of an impeding person,etc. behind the seat 1 in question. The sensor 9 can be of the IR typeor of any other suitable type. Its purpose is to limit or check thechange in position. If a person is sitting behind the relevant seat 1when a collision occurs, this person will be subjected to a risk ofinjury by the rearward-moving seat 1, so it is important to be able tolimit the rearward movement to reduce the risk of injury. It is alsoconceivable that the rearward movement could be completely prevented.

The preferred embodiment shown in FIG. 11 also illustrates anapplication in the automotive, field. This example shows considerablesimilarities to the previous example, so only the differences betweenthem will be described. In this example, track 6 in intermediate section2 is not essentially completely straight as in the example above, it isalso curved. Track 6 in centre section 2 can comprise one or severaltrack segments, including one or more arc sections with constant orvarying radius which give the desired shape of track 6. The effect ofthe curved track 6 is to give seat 1 an inclination in its rearwardposition, as shown in FIG. 12. This means that an inclination is givento seat 1 and other sections such as backrest 10, head restraint 11 etc.This embodiment can be modified by using a number of different tracksinstead of a single track.

This embodiment and the previous embodiment can also be designed so thatseat 1 together with the device in the preferred embodiment movesbackward after triggering. it should be pointed out that section 2 canbe made thinner than shown in FIGS. 9, 10, 11 and 12. This means thatthe drawings are to be regarded as being principle sketches.

An example of another shock absorber is shown in FIG. 13. The dampingfunction of the shock absorber 8 can also be arranged to vary accordingto the force/acceleration measured by such means as an accelerometer.The accelerometer could be contained in the triggering device 4 andindicates the magnitude of the acceleration of the vehicle, which issubjected to a collision or similar. Once the magnitude of theacceleration has been determined, a control unit sets the shock absorberin such as way as to provide a suitable level of damping. Theaccelerometer and the control unit can be arranged in or adjacent to theshock absorber 8. This can be implemented by providing piston 12 indamper 8 with at least two disks 13, each provided with at least onehole 14. Adjustable damping is obtained as a function of the mutualangle of the two disks 13. When the holes 14 in disks 13 overlap eachother, less damping is obtained and when the holes 14 overlap to alesser extent, more damping is obtained. FIG. 13 shows an examplecontaining two disks 13. One way to arrange the setting of the disks 13is to have at least one of the disks 13 fixed to the shaft 15 of theshock absorber 8 and at least one disk 13 fixed at some angle to sleeve16 of shock absorber 8, which means that rotation of sleeve 16 by meansof motor 17 provides adjustment of the damping. The damping is primarilyintended to be only set once and then to be essentially constant duringthe rest of the damping sequence. Setting takes place before or duringthe start of the rearwards movement.

FIG. 14 shows another way to implement damping. It is based on designingthe shock absorber to give increased damping as the damping movementprogresses. The goal is to give the person in seat 1 more gentlebraking. The gentler braking is mainly achieved by arranging the volume18 in which the damping piston 12 moves to have a narrowing crosssection 19 in the direction of movement of piston 12. This narrowingcross section 19 means that damping increases progressively.

The change in position of seat 1 or parts thereof essentially takesplace at the same time as the change in velocity caused by a collision.

One problem associated with whiplash injuries is multiple-car crashes,where the passenger's head is first thrown back, and then when the carcollides with the car in front, the head is thrown forwards. In such anevent, the currently proposed invention functions excellently and theseat moves back and forwards in a controlled manner to reduce thedeceleration during impact with the car in front.

It should be mentioned that the location of the triggering device,sensors and shock absorber can be arranged in a number of differentconfigurations within the framework of the patent claims, and that theirlocation in the figures are to be regarded as being examples. Inaddition, the invention should be arranged so that the unction of theseat belt and the normal adjustment of the seat are not affected, andthey should function normally. Since the seat belt is mounted on theseat and not on the floor, the seat belt will function during the entirecrash sequence.

What is claimed is:
 1. A device for preventing the occurrence ofwhiplash injuries to an occupant of a vehicle having front and backends, said device comprising: a seat having front and rear sections, theseat being mounted to the vehicle; and at least two rolling devicesattached to the seat; and at least one track having front and rear tracksections, one of the rolling devices positioned in the front tracksection and one of the rolling devices positioned in the rear tracksection and wherein at least one of the track sections has an arcuateshape; and wherein in response to a collision of the vehicle, the seatmoves towards the back end of the vehicle and in an accruate motion inaccordance with the movement of the rolling devices in the front andrear track sections; and wherein as a result of the arcuate motion ofthe seat, the seat has a rearward inclination, and wherein both thefront section and the rear section move downward, but the rear sectionmoves downward a greater distance than the front section, simultaneouslyas the seat moves backward in a horizontal direction, thereby resultingin the rearward inclination of the seat.
 2. The device according toclaim 1 wherein the front track section comprises an arcuate section ofconstant or varying radius.
 3. The device according to claim 1 whereinthe rear track section comprises an arcuate section of constant orvarying radius.
 4. The device according to claim 1 further comprising atriggering mechanism coupled to the seat and arranged to sense theforces or accelerations acting upon the vehicle, wherein if a set forceor acceleration is exceeded, the triggering mechanism permits a linearand arcuate movement of the seat.
 5. The device according to claim 1further comprising at least one dampening element to dampen linear andarcuate movement of the seat in at least one direction.
 6. The deviceaccording to claim 1 when utilized in an application which might allowan individual to be present behind the seat during normal operation,further comprising a sensor arranged to detect the position of theindividual, wherein the sensor limits or checks the linear and arcuatemovement of the seat.
 7. The device according to claim 1 wherein thetrack sections are shaped to initially give the seat a linear motionagainst a direction of travel, followed by a swinging,rearward-inclining movement.
 8. The device according to claim 1 furtherincluding means to damp a change in position of the seat.
 9. The deviceaccording to claim 1 further including a sensor to detect a personlocated behind the seat and further including means that, in response todetecting the person, limit or prevent a change of position of the seat.10. A device for preventing the occurrence of whiplash injuries to anoccupant of a vehicle having front and back ends, said devicecomprising: a seat having front and rear sections, the seat beingmounted to the vehicle, and at least two rolling devices attached to theseat; and at least one track having front and rear track sections, oneof the rolling devices positioned in the front track section and one ofthe rolling devices positioned in the rear track section and wherein atleast one of the track sections has an arcuate shape; and wherein inresponse to a collision of the vehicle, the seat moves towards the backend of the vehicle and in an arcuate motion in accordance with themovement of the rolling devices in the front and rear track sections,and wherein as a result of the arcuate motion of the seat, the seat hasa rearward inclination, and wherein both the front section and the rearsection move upward, but the front section moves up more than the rearsection, simultaneously as the seat moves backward in a horizontaldirection, thereby resulting in the rearward inclination of the seat.11. The device according to claim 10 wherein the front track sectioncomprises an arcuate section of constant or varying radius.
 12. Thedevice according to claim 10 wherein the rear track section comprises anarcuate section of constant or varying radius.
 13. The device accordingto claim 10 further comprising a triggering mechanism coupled to theseat and arranged to sense the forces or accelerations acting upon thevehicle, wherein if a set force or acceleration is exceeded, thetriggering mechanism permits linear and arcuate movement of the seat.14. The device according to claim 10 further comprising at least onedampening element to dampen linear and arcuate movement of the seat inat least one direction.
 15. The device according to claim 10 whenutilized in an application which might allow an individual to be presentbehind the seat during normal operation, further comprising a sensorarranged to detect the position of the individual, wherein the sensorlimits or checks linear and arcuate movement of the seat.
 16. The deviceaccording to claim 10 wherein the track sections are shaped to initiallygive the seat a linear motion against a direction of travel, followed bya swinging, rearward-inclining movement.
 17. The device according toclaim 10 further including means to damp a change in position of theseat.
 18. The device according to claim 10 further including a sensor todetect a person located behind the seat and further including meansthat, in response to detecting the person, limit or prevent a change ofposition of the seat.